Soil is a component of the environment and sustains growth of several plants and animals.
It forms part of the biosphere and can be described as the interface between the
atmosphere and the lithosphere. The interaction between soil, climate and topography and
the resulting agricultural aptitude forms the concept of terroir. This relationship is complex
and it is difficult to quantify the contribution of each.
Grapevines are exposed to an array of soil types. Soils have varying colours, which can be
ascribed to their origin from different parent materials and pedogenetic factors. Historical
and experimental evidence points to the key role that soil physical conditions play in
determining grape berry composition, but other soil related factors may also play a role.
This study was conducted to investigate the effect of soil surface colour on the vegetative
and reproductive growth characteristics of Cabernet Sauvignon. The aim was to determine
whether a relationship exists between soil colour, reflective light quality below and inside
the grapevine canopy, vegetative growth of the grapevine and the berry and wine
composition.
The reflected light from soils was measured in three positions of the canopy and across
the light spectrum (300–2500 nm) for three different soil surface treatments (black, red and
grey). The effect of soil colour on vegetative parameters, yield and berry composition and
wine quality was investigated. Soil surface colour resulted in differences in the reflected
light quality below and in the canopy. The differences in the light quality were associated
with differences in vegetative parameters such as mean main leaf, with grey soils inducing
higher values. Potassium levels of the grapes and berry number per bunch appeared to be
influenced by soil surface colour throughout berry development with red and black soils
having higher levels of potassium and berry number per bunch than grey soils. Grape
ripening parameters were not influenced by soil surface colour, but the grey treatment had
a significantly more intense grape colour measured at 520 nm (red pigments).
It is assumed that the importance of soil colour is its association with the physical and the
pedogenetic properties that contribute to the grapevine water balance. From these results it can be concluded that soil surface colour appeared to have a direct effect on some
aspects of vegetative and reproductive growth, and berry composition, but the contribution
of different wavebands and mechanism of their effect deserves further study.

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en

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Stellenbosch : Stellenbosch University

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Soil surface colour

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Light quality

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Light quantity

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Reflectance

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Terroir -- South Africa -- Stellenbosch

en

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Viticulture -- South Africa -- Stellenbosch

en

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Soils -- Color -- South Africa -- Stellenbosch

en

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Plant-soil relationships

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Dissertations -- Africulture

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Theses -- Agriculture

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Dissertations -- Viticulture and oenology

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Theses -- Viticulture and oenology

en

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The ecophysiological characterisation of terroirs in Stellenbosch : the contribution of soil surface colour